An electric or electric power-assisted bicycle is welcomed as a kind of new transport tool to replace walking. However, the electric wheel hub installed on its front and rear wheels directly drives most of current electric power-assisted bicycles. The drawbacks of this structure are listed as follows.
Firstly, the wheel hub equipped with motor and reducer increases the weight of the front or rear wheel, which affect the positions of gravity center, stability and wheel structure designed for the common bicycle.
Secondly, the ratio of the reducer in wheel hub can not be adjusted, while the speed regulation mode of common bicycle is not available for electric bicycle. Then its motor has to run at low speed to regulate the speed, which will not release the full power of the motor; it is not perfect in the whole structure and human engineering design, also in the assembling, using, maintaining and so on.
Furthermore, though they are installed near the center shaft, the bicycle is also discommodes to carry due to the weight and volume of common motor and gear reducer.
In view of the deficiencies of the structure of the prior art of an electric or electric power-assisted bicycle, it is thus an object to provide a kind of electric or electric power-assisted bicycle, which basically keeps the structure and the position of gravity center of common bicycle. It's electric-driving device having small volume, lightweight and high-speed ratio, while it is also energy saving, high efficient and can be conveniently assembled, used and maintained.